Preformed pavement marking materials are used as traffic control markings for a variety of uses, such as short distance lane striping, stop bars, and pedestrian lane markings at intersections. Typically, preformed pavement marking materials comprise a continuous, wear-resistant top layer overlying a flexible base sheet. Such materials are applied to substrates using pressure sensitive adhesive or contact cement.
For example, U.S. Pat. No. 4,020,211 discloses a preformed marking composite material comprising a continuous polyurethane top layer adhered to a flexible base sheet. These marking materials have a very high Young's modulus, well above 300,000 psi. As a result, these materials are so stiff and nonconformable that the entire composite material tends to come loose from irregular pavement surfaces due to poor adhesion to the pavement.
A more conformable preformed marking material comprising a more elastic, continuous polyurethane wear layer adhered to a flexible base sheet is described in assignee's copending application, U.S. Ser. No. 07/372,183 filed June 26, 1989, which is a continuation of U.S. Ser. No. 06/866,570, filed May 29, 1986, now abandoned. Similar materials are also described in U.S. Pat. Nos. 4,248,932; 4,117,192; 3,935,365; and in European Patent Application No. 0,162,229. These materials have better initial conformance to irregular pavement surfaces due to the lower modulus of the polyurethane wear layer. The elastic nature of the polyurethane wear layer, though, produces elastic tensile stresses in the top layer as these marking materials are adhered and conformed to the pavement. Over time, these stresses tend to cause adhesive failure, after which the marking materials would come loose from the pavement.
Assignee's copending application, U.S. Ser. No. 07/204,349, filed June 9, 1988, describes a pavement marking material comprising a polyurethane bead bond overlying a flexible base sheet having protrusions on one surface. The bead bond covers selected portions of these protrusions. One bead bond disclosed is a polyurethane urea comprising about two equivalents of bis (4-cyclohexyl isocyanate) (H.sub.12 :MDI) and about one equivalent of a polycaprolactone triol having a molecular weight of about 540 and a hydroxyl number of about 310.